1. Field of the Invention
The present invention relates to: a graphic processing method, device, and program recording medium; particularly a method for comparing shapes of figures; especially a shape comparison method and a shape inspection method in which outline shapes extracted from a digital image of an object acquired by a microscope or a digital image of a fine pattern acquired by an electronic microscope are compared or inspected; and further a graphic processing method including a program for realizing the method, a device, and a recording medium of a graphic processing program.
2. Background Art
There have heretofore been proposed a large number of techniques for quantizing shapes of objects reflected in general digital images acquired by digital image forming means including an electronic microscope, an optical microscope, a digital camera, a video camera and the like. Above all, as a method for judging whether or not the shape is satisfactory, a method has been frequently used in which a reference image is compared with an inspection object image, and a difference between the images is quantized to judge whether or not the shape is satisfactory.
As a quantization method, a method using a correlation function between images has been used long. The method is described in Chapter 8, Section 3, “digital Picture Processing (Academic Press, Inc. 1976)” authored by A. Rosenfel and A. C. Kak, which has already been a classic document. A function of using a value of cross correlation described in the document as a scale of similarity between the images has been incorporated as a standard into an image processing system these days, but there has been a problem that the function is largely influenced by a fluctuation of light and shade of a whole image to be treated or noise.
To solve the problem, in recent years, a method has been frequently used in which the outline of a target object included in an image is extracted, and the shape of the object is quantized or compared with a reference shape in various methods. As concrete document examples, a method in which direct template matching of numerical value data of outlines is combined with similarity transformation of a coordinate is described, for example, in U.S. Pat. Nos. 6,563,324, 5,845,007, and 5,796,868.
In these methods, it can be judged whether or not there is a difference between a reference figure and an inspection object figure, but it has been difficult to determine statistical significance concerning the difference. There has also been a problem that quantization of the difference between the figures is influenced by an error in positioning the figures.
Moreover, a method in which the outline shape is subjected to coordinate transformation to extract a characteristics amount is described, for example, in U.S. Pat. No. 3,069,654. However, there has been a problem that the method is not effective in a case other than a case where a reference figure includes circular or linear components.
Furthermore, a method in which the outline coordinate is subjected to Fourier transformation, and Fourier coefficients (Fourier descriptors) are compared to compare the shapes is described in C. T. Zahn and R. Z. Roskies: IEEE Transactions on Computers, Vol. C-21, pp 269 to 281 (1972), G. H. Granlund: IEEE Trans. Computers, C-21, pp 195 to 201 (1972), Y. Uesaka: Transaction of IEICE Vol. J67-A, pp 166 to 173 (1984), Computer Graphics and Image Processing, Vol. 18, pp 236 to 258 (1982) and the like. Application of this technique to inspection of a pattern of a semiconductor is described in Japanese Patent Application Laid-Open No. 2003-031469. In these methods, a property that scales such as Fourier descriptors are universal is used. Therefore, a reference figure can be compared with an inspection object figure without being influenced by the positioning error. On the other hand, there has been a problem that an scaling error of both the figures cannot be known.
Moreover, even when there is a difference between the obtained Fourier descriptors, it has been still difficult to determine the statistical significance. A method in which a figure prepared by simulation of design data for use in a computer aided design system (CAD), mask data prepared in preparing a photo mask in a semiconductor field, or a pattern shape obtained from the data through a pattern forming step is used as a reference figure is described in Japanese Patent Application Laid-Open Nos. 2000-293690, 2002-031525, 2001-338304 and the like.
Moreover, a method in which the Fourier descriptor of the design data or the figure prepared by the simulation is used as the reference, and compared with that of an actual pattern outline is described in the Japanese Patent Application Laid-Open No. 2000-293690. However, it is still difficult to determine the statistical significance of the difference between the figure shapes even by these methods. In the above-described methods other than the method of the Japanese Patent Application Laid-Open No. 2000-293690, it is difficult to eliminate the influence of the positioning error of both the figures. In the method of the Japanese Patent Application Laid-Open No. 2000-293690, it has been still impossible to consider the influence of the scaling error.
An object of the present invention is to provide a graphic processing method, device, and program recording medium capable of representing a difference between two figures in a method in which a significant difference can be determined, reducing an influence by a positioning error which has heretofore been a problem, and correctly considering the influence of a scaling error.